A method and an apparatus for applying an emulsion onto a screen-printing plate

Abstract

 A method and an apparatus for applying an emulsion onto a screen-printing plate are disclosed, in which an emulsion film having thereon an applying emulsion of a predeermined thickness is prepared, which film is closely contacted with the screen-printing plate on its printing side for applying the emulsion thereon. Preferably, a penetrable agent is supplied for facilitating the release and adhesion of the applying emulsion.

Description

[0001] This invention relates to a"'method and an apparatus for applying an emulsion onto a screen-printing plate, wherein upon applying the emulsion of a photosensitive material onto the screen-printing plate an emulsion film coated with a predetermined thickness of the emulsion is utilized for achieving a uniform thickness of the emulsion over the entire surface of the screen on its printing side and sharp print lines on printings.

[0002] Heretofore, the emulsion has been applied by vertically slidable squeegees of a bucket type having contacted at their front edges with the screen consisting of a screen material of silk, polyester, nylon or the like of a given mesh size and a frame surrounding the screen material. In this case, manual moving operation requires a particularly high skill for applying a film of a uniform thickness. In order to overcome the difficulty of the prior art, there have been proposed various types of mocha-nically moving squeegees, as disclosed in U.S. Patent 4363289 (corres. to the Published European Patent Application 0026538). The U.S. Patent relates to a method and an apparatus for applying an emulsion onto a screen printing, in which squeegees arranges at either side of the screen are advanced toward the screen face for contacting therewith, inclined for flowing the emulsion out of the squeegees at their front edges, and vertically moved relative to the screen. With this prior art, the emulsion flows down naturally from, the squeegees, so that the emulsion may be scraped by the front edge of the squeegee upon its upward movement for providing a uniform film thickness, whereas upon its downward movement (necessary for thick application) the emulsion may flow into the underside of the squeegee and is applied in different quantities thereby to provide a much irregular thickness. Upon application with the emulsion on both sides of the screen from its lower section, a certain distance between the screen face and the front edges of the squeegees is needed for giving a relatively thick emulsion film, because the contacted squeegees may scrape off the applied emulsion. Thus, the screen with a larger thickness of the emulsion on its printing side can not be produced. Further, the squeegees on both sides of the screen are symmetrically moved synchronously with each other by a single cylinder, so that one of the squeegees must be replaced by a rod or roller for application only on a single side of the screen, requiring a troublesome replacement and resulting in a very difficult switchover of the application from both sides to the single side of the screen or vice versa through continuous and automatic operation. Upon printing with the screen, application of the more thick emulsion on the printing side than on the ink-applying side is essential for obtaining a beautiful print, which is difficult to be achieved by the prior art as described hereinabove.

[0003] Further, another method has hitherto been employed in which an applying film having layered thereon a predetermined thickness of an emulsion is releasably coated on a substrate to form an emulsion film which in turn is set horizontally under a screen face, and in which a suitable squeegee is used for manually coating the applying film on the screen face in order to penetrate the emulsion from the screen with a penetraing agent, such as water. In this method, however, the manual movement of the squeegee provides ununiform penetration of the agent into the whole area of the applying film to leave non-attached portions thereon after the operation, so that a skillful applying operation is required.

[0004] Accordingly, an object of the invention is to solve the problem in the prior method and apparatus and to provide a method and an apparatus capable of variably determining a thickness of an emulsion on a printing face of a screen by selecting a thickness of an applying film, an 'applying pressure of a squeegee for feeding a penetrating agent onto the applying film, a feeding rate of the penetrating agent, and a type of the penetrating agent, and further providing uniform and sharp lines upon printings.

[0005] In one aspect, the invention provides a method of applying an emulsion onto a screen printing plate supported vertically on a base, which comprises the steps of: providing an emulsion film having releasably coated on its substrate with a penetrable film of an emulsion of a predetermined thickness, keeping the emulsion film on its coated surface in contact with the screen-printing plate on its printing side, applying the penetrable film thereon by means of a squeegee which is vertically movable on the inking side of said screen-printing plate, adhering the penetrable film to the screen surface through penetrating action of the emulsion, and removing the substrate released therefrom.

[0006] In another aspect, the invention provides an apparatus for applying an emulsion onto a screen-printing plate, which comprises a base having opposite vertical side walls on its either side for forming a frame; a supporting mechanism for supporting an emulsion film in contact with a supporting plate fixed vertically to the base and having clamps for urging the planar screen-printing plate against the emulsion film at its front face, said emulsion film having a substrate coated releasably with a predetermined thickness of a penetrable film of emulsion; a lifting mechanism for vertically moving an applying element along the screen-printing plate on its front side, said applying element holding a penetrable material for the film; an actuating mechanism arranged at the front of the screen-printing plate for advancing the applying element toward the screen face during upward movement of the applying element, thereby to allow its front edge to be contacted with the screen face and to be inclined, and for restoring the applying element to its horizontal state upon downward movement for retreating from the screen face; and a controlling mechanism for controlling said various movement of the applying element.

[0007] The invention will be described hereinbelow in more detail for the preferred embodiments with reference to the accompanying drawings.

[0008] 

Figure 1 is a schematic side view showing the applying operation according to the invention;

Figure 2 is a schematic side view showing another embodiment of the applying operation according to the invention;

Figure 3 is a plan view of the apparatus according to the invention;

Figure 4 is a vertical section of the apparatus of Fig. 3;

Figure 5 is a vertical section of a main portion of the apparatus;

Figure 6 is a cross-section of the main portion of the apparatus;

Figure 7 is a pneumatic circuitry in a controlling mechanism for the apparatus according to the invention; and

Figure^-8 is a vertical section of another embodiment of the apparatus according to the invention.

[0009] In Figs. 1 and 2, an emulsion film 1 has releasably coated on a substrate 2 of a plastic sheet with a penetrable film 3 of a photo-sensitive emulsion in a predetermined thickness corresponding to a thickness of an emulsion to be applied onto a screen-printing plate S, which consists of a frame P and a screen material M surrounded thereby and made of a silk, polyester, nylon or stainless screen having a predetermined mesh size. The thickness may be in the order of 15, 20, 25, 30 in consideration of an amount to be incorporated into the screen material M.

[0010] The emulsion film 1 is contacted on its applying side 3 with a printing side (or a printing surface) of the screen-printing plate S supported vertically. In such position, the screen material M is applied with a penetrating agent D by a bucket sgueegee 25 vertically moving along an inking side (or a squeegee side) of the screen-printing plate S. A penetrating action of the agent D into the film 3 enables the latter to be adhered onto the screen surface. The penetrating agent D is penetrated into the film 3 for dissolving the same and may be water or a photosensitive emulsion or a combination thereof.

[0011] When the agent D is applied by the squeegee 25 onto the screen M, a predetermined pressure is given to the screen M, so that an enough supporting force is required to keep the emulsion film 1 in contact with the screen material M. For this purpose, the emulsion film 1 may be supported on its rear face (or substrate side) by a suitable supporting means.

[0012] One embodiment of the supporting means as shown in Fig. 1 is a supporting element 25A which is movable along the screen face synchroneously with vertical movement of the squeegee 25. The supporting element 25A is located in a retreated position before the applying operation, but advances synchroneously with squeegee 25 for urging the emulsion film 1 onto the screen M (see Fig. 1 (2) ) and pouring the penetrable agent D by tilting the squeegee 25 (see Fig. 1 (2) and (3) ). In this case, the emulsion film 1 at its upper end is manually held by operator's fingers or other subsidiary supporting means. This type of the supporting element has an advantage in that the squeegees 25 of the same type may be utilized on either side of the screen-printing plate S and in that the screen-printing plate S may be set irrespective of its front or rear face.

[0013] Another embodiment of the supporting means as shown in Fig. 2 is a plate element 25B for holding the whole surface of the emulsion film 1 in contact with the screen M. The plate element 25B may be set by means of clamps 26 at a time when the screen-printing plate S is assembled, and may be rectangular place covered with a cloth. In this embodiment, the plate element 25B is secured to the rear side of the screen M in order to hold the emulsion film 1 in contact with the screen M prior to the squeegee operation (see Fig. 2 (1) ). Then, the squeegee 25 is advanced and tilted while moving upwardly to pour the penetrable agent D (Fig. 2 (2) and (3) ). The plate element 25B has an advantage of improving the operability without need for the subsidiary suppporting element as in the first embodiment.

[0014] After the applying film 3 of the emulsion film 1 is contacted with the screen M in this way, only the substrate 2 is released from the emulsion film 1 to leave the emulsion (namely, the applying film 3) of the predetermined thickness on the screen M.

[0015] The apparatus according to the inventin for embodying the method as described hereinabove will be illustrated in detail with reference to Figs. 3 to 8.

[0016] The apparatus according to the invention comprises a base 10 arranged on a suitable location, a supporting mechanism 20 for vertically supporting the screen-printing plate S in contact with the emulsion film 1, an applying mechanism 40 for lifting an applying element 35 in front of the screen-printing plate S in order to provide the penetrable agent D, and a controlling mechanism 70 for adjusting the supply of the penetrable agent D by the applying element 35.

[0017] As shown in Fig. 3, the base 10 is provided vertically with opposite walls 12, 13 which are adjusted horizontally by an adjuster 15 and provided with an upper wall 14 therebetween. In front of the wall 12 is arranged an operation panel 72, 73 as described hereinafter which has previously been set for various factors of the controlling mechanism 70. In a lower space is received a motor 41 for driving the applying mechanism 40.

[0018] In an operational space between the walls 12 and 13 are arranged the supporting mechanism 20, the applying mechanism 40 and an operational mechanism 50, respectively for setting the screen-printing plate S with the emulsion film 1, and applying the penetrable agent D to form the applying film 3 on the screen material M.

[0019] As shown in Figs. 3 and 4, the supporting mechanism 20 consists of a supporting plate 22 vertically secured to the base 10 between horizontal supporting bars 21 and of clamps 26 for holding and press-fixing the emulsion film 1 in contact against the screen-printing plate S. For this supporting purpose, the lower bar 21 is provided with clamping dies 24 which at their rear face are inclined as shown in Fig. 4, while a vertically slidable clamp-fixing bar is arranged in front of the supporting plate 22, which bar is provided with clamps 26 of a pneumatic cylinder type each having a grip with its rear face being inclined. Thus, the screen-printing plate S is set between the supporting plate 22 and the dies 24. Operation of the clamp 26 allows each inclined face of the dies 24 and the clamps 26 to urge the screen-printing plate S toward the supporting plate 22, thereby to hold the screen material M of the screen-printing plate S in contact with the emulsion film 1 on the supporting plate 22. Thus, the reliable setting may be achieved by the simple construction.

[0020] The supporting plate 22 on its front face is attached with an elastomeric mat 23 which may be rubber or other elastomers in a sheet form of a predetermined thickness. When the mat 23 is contacted with the emulsion film 1, an electro-static action may support these elements at a required position without need for special subsidiary fixing means. When the penetrable agent D is supplied to the screen material M by the supplying element 35 for applying the emulsion 3 of the emulsion film 1 onto the screen material M, the element 35 urges the screen M with a required force and moves upwardly. In this case, an elastic action of the mat 23 may impart-an adequate tension to the screen material M, thereby to achieve smooth movement of the element 35 along the screen face.

[0021] Figure 8 shows another embodiment, in which a film feeding mechanism 30 is arranged for receiving a wound roll of the emulsion film 1 to be cut in a required length upon use. The film-supplying mechanism 30 consists of a feeding roller 31 arranged between the walls 12 and 13 for replaceably receiving the wound roll of the emulsion film 1. Thus, the emulsion film 1 may be fed continuously and used in any suitable length to improve the operability.

[0022] In such contacted relation of the emulsion film 1 with the screen-printing plate S, the penetrable agent D is applied from the printing side of the plate S by the applying mechanism 40 and the operational mechanism 50.

[0023] The applying mechanism 40 enables the supplying element 35 to move vertically along the screen face. More particularly, a supporting bar 55 removably supporting the supplying element 35 is arranged between opposite units 45, 45 on the walls 12 and 13, each of which units is engaged with a chain 44 recycling in the respective wall 12, 13 and is moved vertically by means of a guide roller 47 along a guide 42. Above and below the guide 42 are arranged sprockt wheels 43 which are engeged with the chain 44. Thus, the chain 44 may be driven by the motor 41 for moving the unit 45. The moving range of the unit 45 may be adjusted in a distance between the upper and the lower ends of the screen-printing plate S on the supporting mechanism 20. Therefore, the corresponding positions of the walls 12, 13 are provided with an adjustable upper and lower limiting switches 48, 48 for deenergizing the motor 41 upon contact with the unit 45. As shown in Fig. 6, the chain 44 behind the guide 42 is engaged with an engaging part 46 protruded behind the unit 45. The engaging part 46 is provided with a guide roller 47 in contact with a front edge of the guide 42, which roller is rotated along the guide 42 to vertically move the unit 45 smoothly in association with the chain 44 and thus to ensure a constant pressure and distance of the supplying element 35 in relation to the screen face. Preferably, a shock- or vibration-absorbing material may be inserted between the guide 42 and the guide roller 47.

[0024] The applying mechanism 50 permits the supplying element 35 to advance toward the screen face upon upward movement of the element 35 and to put its front edge in a contacted and inclined position, while the mechanism 50 permits the supplying element 35 to restore its horizontal. position and to retreat from the screen face upon downward movement of the element 35.

[0025] More particularly, the applying mechanism 50 comprises tilting arms 52 swingably supported to the units 45 movable along the walls 12 and 13, between which arms 52 is arranged the supporting bar 55. The tilting arms 52 may be slided forward and backward by a slide shaft 54 attached thereto. The supporting bar 55 is connected to a piston 58 of a cylinder 57 fixed to the tilting arm 52, while the tilting arm 52 is connected to a piston 61 of a cylinder 60 supported:to the unit 45.

[0026] As shown in the drawings, when the applying element 35 mounted to the supporting bar 55 applies the penetrable agent D, it advances toward the screen face to contact at its front edge with the screen face and tilts for pouring the penetrable agent D, which in turn passes through the screen mesh to penetrate the emulsion film 1. For this reason, the applying element 35 is desirably,inclined with its front edge being fixed. In order to advance the applying element 35 rapidly and smoothly toward the screen face, the supporting bar 55 is arranged between the arms 52 for ensuring that the front edge is aligned with a supporting position of the arm 52 after completing the advancing movement. For this purpose, the applying element 35 is operated by serving a contacted point of the screen as a tilting center, while the supporting position of the tilting arm 52 is located on a supporting pin 51 in the unit 45.

[0027] As shown in Figs. 5 and 6, the arm 52 is provided with a pair of supports 53, between which a slide shaft 54 is arranged. Under the front support 53 is horizontally arranged a cylinder 57, a piston 58 of which is extended in parallel to the slide shaft 54. A front end of the piston 58 is connected to a joint 59 provided under the supporting bar 55. Under the arm 52 is vertically arranged a cylinder 60 which is connected to the unit 45 and a piston of which at its front end is connected to the arm 52. The supporting bar 55 is fitted to the slide shaft 54 through a ball bushing 56 formed at either end of the bar 55. Thus, the bar 55 is arranged between the arms 52 supported to the units 45. By using the ball bushing 56, the supporting bar 55 may be moved smoothly along the slide shaft 54 with less friction. Further, the long bar 55 may be prevented from deflecting and ensure the stable operation.

[0028] The applying mechanism 50 thus constructed is operated by a controlling mechanism 70 as described hereinafter. When the unit 45 moves upward, the cylinder 57 is operated to advance the supporting bar 55 on the slide shaft 54 for urging the front edge of the applying element 35 against the screen face (see Figs. 4 and 5). Then, the cylinder 60 is operated to tilt the arm 52 together with the applying element 35 for pouring the penetrable agent D onto the screen M. When the unit 45 moves downward, the cylinder 60 is operated to restore the arm 52 together with the applying element 35 to the horizontal position and then the cylinder 57 is operated to retreat the supporting bar 55 with the applying element 35.

[0029] The apparatus according to.the invention is provided with the controlling mechanism 70 comprising an electric, hydraulic or pneumatic circuit for controlling the vertical movement of the applying element 35 as well as the advancing, tilting, restoring and retreating movement of the applying element 35. As shown in Fig. 7, the controlling mechanism 70 may control the supply, exhaust and interruption of pneumatic air to the cylinders 57 and 60. In Fig. 7, references 74, 75, 76, 77 and 78 represent a vacuum unit, a switch valve, a muffler, a reducing valve and a speed controller, respectively. As shown in Fig. 3, these elements may be controlled by various buttons and dials arranged on an electrically operating panel 72 and a pneumatically operating panel 73. If desired, the applying number and setting may be automatically established by selecting the combination of the elements.

[0030] The operation of the apparatus according to the invention will be described with reference to Figs. 3 to 6.. At first the emulsion film 1 of a size corresponding to the screen-printing plate S is prepared. The applying film (emulsion) 3 is supported in front of the supporting plate 22 in contact therewith, while the printing fact of the screen-printing plate S is contacted with the applying film 3. In this position, they are vertically suported and fixed by the clamps 26. On the other hand, the applying element 35 attached to the supporting bar 55 is filled with the penetrating agent D and is operated by various buttons and a starting switch 71 on the operating panel 72. The applying mechanism 50 starts to operate the cylinder 57 for advancing the supporting bar 55 and the applying element 35 toward the screen face and contacting the applying element 35 at its front edge with the screen face. Thereafter, the cylinder 60 is operated to tilt the applying element 35 for pouring the penetrable agent D onto the screen face. In this case, a variable timer has been set for time enouth to allow the penetrable agent D to penetrate into the screen M. Then, the mechanism 40 is operated to lift the unit 45 by the chain 44, thereby to lift the supporting bar 55 together with the applying element 35 while pouring the agent D onto the screen. Upon reaching the predetermined position, the applying element 35 discontinues its upward movement and the cylinder 60 is reoperated to restore the element 35 to its horizontal state. If desired, the element 35 continues its upward movement for scraping and recovering the agent D. Then, the cylinder 57B is operated to retreat the element 35 from the screen face, while the mechanism 40 is reversely operated to lower the unit 45 and the element 35, thereby to restore its initial position.

[0031] If necessary, the applying operation may be repeated several times which have been set in the controlling mechanism. In this case, the applying numbers may be automatically counted. After the predetermined numbers, the applying operation may be discontinued automatically.

[0032] Thus, the penetrable agent D is applied to the squeegee side of the screen-printing plate S and penetrates through the screen M into the emulsion 3 of the emulsion film 1 to provide a suitable viscosity for adhering to the printing face of the screen material M. After the applying operation for the penetrable agent D, the supporting mechanism 20 is released to remove the screen-printing plate S and thereafter the substrate 2 of the emulsion film 1 is removed to complete the printing screen.

[0033] In accordance with the invention, the emulsion film of a predetermined thickness may be applied onto the screen face, depending on the thickness of the applying film 3 of the emulsion film 1, the applying pressure of the supplying element 35 and its speed. Further, the application of the emulsion is promoted by the action of the penetrating agent on the applying film 3 during the upward movement of the element 35, so that the emulsion may be adhesively applied to the screen face. By preparing the emulsion film 1 having the applying film 3 of a thickness corresponding to the thickness of the emulsion required for the screen-printing plate S, by selecting the applying pressure and speed of the squeegee 25, the supporting means 25A and 25B as well as the penetrating agent D, and by controlling the applying mechanism 40, and the operational mechanism 50 by means of the controlling mechanism 70, the emulsion of the proper thickness may be formed on the printing side of the screen-printing plate S. Further, the penetrating agent D is penetrated uniformly and adequately throughout the whole area of the screen face, so that the more smooth emulsion membrane may be obtained.

[0034] Particularly, the supporting mechanism 20 may support the emulsion film 1 in close contact with the supporting plate 22 on the base 10, while the clamps 26 may fix the emulsion film 1 to the flat screen-printing plate, so that the emulsion film 1 may be adhesively contacted with the screen-printing plate S. When the applying element 35 is moved upward in contacted with the screen face M by the lifting mechanism 40 and the operational mechanism 50, the penetrable agent D carried in the applying element 35 may penetrate through the screen M uniformly into the applying film 3 to form the even and smooth emulsion membrane on the screen-printing plate S. Further, the supporting plate 22 may support the flexible emulsion film 1 securely to the screen-printing plate S and the applying element 35 may smoothly moved upward, thereby to improve the workability.

[0035] The applying mechanism 50 enables the applying element 35 to move toward the screen face M during its upward movement and to be contacted in its inclined position with the screen face. During the downward movement, the applying element 35 may be restored to its horizontal position and retreated from the screen face. Thus, the penetrable agent D may be applied only during the upward movement of the applying element 35, thereby to ensure the constant supply of the penetrable agent, the prevention of the fluid loss during the application and the smooth formation of the emulsion membrane.

[0036] As described hereinabove, in accordance with the invention, the uniform emulsion membrane of the predetermined thickness may be formed on the screen-printing plate without the conventional troublesome and complicated operation. In addition, the more sharp print lines and hence the excellent printings may be produced.

Claims

1. A method of applying an emulsion onto a screen printing plate supported vertically on a base, which comprises the steps of:

providing an emulsion film having releasably coated on its substrate with a penetrable film of an emulsion of a predetermined thickness,

keeping the emulsion film on its coated surface in contact with the screen printing plate on its printing side, applying the penetrable film thereon by means of a squeegee which is vertically movable on the inking side of said screen-printing plate,

adhering the penetrable film to the screen surface through penetrating action of the emulsion, and removing the substrate released therefrom.

2. The method as claimed in claim 1, wherein the penetrable material is composed of an aqueous or liquid emulsion.

3. The method as claimed in claim 1 or 2, wherein the emulsion film is kept in contact with the screen surface by means of a supporting element which is vertically movable in synchronization with vertical movement of the squeegee.

4. The method as claimed in claim 1 or 2, wherein the emulsion film is kept in contact with the screen surface by means of the plate element having an applying surface area.

5. An apparatus for applying an emulsion onto a screen printing plate, which comprises a base having opposite vertical side walls on its either side for forming a frame; a supporting mechanism for supporting an emulsion film in contact with a supporting plate fixed vertically to the base and having clamps for urging the planar screen-printing plate against the emulsion film at its front face, said emulsion film having a substrate coated releasably with a predetermined thickness of a penetrable film of emulsion; a lifting mechanism for vertically moving an applying element along the screen-printing plate on its front side, said applying element holding a penetrable material for the film; an actuating mechanism arranged at the front of the screen-printing plate for advancing the applying element toward the screen face during upward movement of the applying element, thereby to allow its front edge to be contacted with the screen face and to be inclined, and for restoring the applying element to its horizontal state upon downward movement for retreating from the screen face; and a controlling mechanism for controlling said various movement of the applying element.

6. The apparatus as claimed in claim 5, wherein a mat of an elastic material is attached to the supporting plate at its front face.

7. The apparatus as claimed in claim 5 or 6, further comprising a film feeding mechanism having received therein the wound emulsion film to be cut in a required length for use.

Drawing